The present invention relates to a diaphragm carburetor for an internal combustion engine, especially for an internal combustion engine in a portable, hand-guided working tool such as a motor chain saw etc., comprising a fuel-filled control chamber that is supplied via an inlet valve from a fuel reservoir and comprising a main valve channel connecting the control chamber to a venturi section of the suction channel. The main valve channel has a check valve that closes the main valve channel in the direction towards the control chamber and is arranged in the vicinity of the control chamber.
From German Patent Application 195 09 943 a diaphragm carburetor of the aforementioned kind is known having a control chamber that is connected by an idle system as well as the main valve channel to the suction channel and the internal combustion engine. At the outlet opening of the main channel the valve plate is arranged which closes the outlet opening in the manner of a check valve when in the idle position due to the vacuum level in the control system a return flow of air into the control chamber would be possible. Due to the engine vibrations to which the carburetor is subjected in idle position, the check valve plate is pressure-loaded by the fuel column positioned thereat so that in certain operational situations fuel can exit via the main valve which may result in great fluctuations of the idle rpm. In extreme cases, when the mixture is too rich, the internal combustion engine will stop.
It is known to guide the fuel flow from the control system to the venturi section via channels, transverse bores, or other throttle locations. These systems, under full load of the engine, exhibit considerable fluctuations during operation.
It is therefore an object of the present invention to improve a diaphragm carburetor of the aforementioned kind such that with a simple embodiment of the main valve channel the vibrations resulting from the engine will not result in opening of the check valve in the main valve channel.